1. Field of the Invention
The present invention relates to a sheet feeding apparatus for feeding sheets one-by-one, for example to an image forming unit of a printer, a facsimile machine, a copying machine or the like. The invention is more particularly related to a sheet feeding apparatus in which both a paper tray and a separating member which is a frictional surface are separable from a feed roller.
2. Description of the Background
FIG. 10 is an illustration showing an example of a sheet feeding apparatus in a conventional electrophotographic image forming apparatus. A sheet feeding and separating roller 3 which separates and feeds an individual sheet 2 stacked on a paper tray 1 is in pressured contact with a sheet separating member 4 for preventing a double feeding of the sheet 2. A pair of registration rollers 5, a photoconductive drum 6, a transfer roller 7 and the like are disposed downstream in a feeding direction of the sheet 2 of the sheet feeding and separating roller 3.
When the sheet feeding and separating roller 3, the registration rollers 5 and the like are rotatably driven at the start of an image forming operation, the sheet 2 stacked on the tray 1 is fed from the top of the stack towards the sheet separating member 4 by a frictional force of the sheet feeding and separating roller 3 against the sheet 2. If the single sheet 2 is fed, the sheet 2 is fed between the sheet feeding and separating roller 3 and the sheet separating member 4 by the rotational force of the roller 3. However, if more than one sheet is fed from the tray 1, the sheet separating member 4 applies a larger friction force to the lower sheet 2 than the frictional force between the two sheets. Therefore, only one sheet at a side of the sheet feeding and separating roller 3 is fed towards the registration rollers 5 and any other sheets remain unfed.
The sheet 2 separated by the sheet separating member 4 is conveyed to a nip of the photoconductive drum 6 and the transfer roller 7, at a proper time by the registration rollers 5, and a toner image formed on the photoconductive drum 6 is transferred on the sheet 2.
Further, a sheet feeding apparatus disclosed in Japanese Laid-open Utility Model application No. 39841/1994 is explained based on FIG. 11. In this sheet feeding apparatus, a sheet feeding roller 10, made of a material such as rubber feeds a sheet 9 mounted on a tray 8. The sheet feeding roller 10 has a sector shape, and a driven sheet conveying roller 12 is mounted rotatably on a rotating drive shaft 11 of the sheet feeding roller 10. An independent rotating drive shaft 13 is disposed parallel to the rotating drive shaft 11, and a drive sheet conveying roller 14 which contacts the driven sheet conveying roller 12 with pressure is fixed to the shaft 13. Further, a separating member 15 is held rotatably around the rotating drive shaft 13, and the separating member 15 touches the outer peripheral surface of the driven sheet conveying roller 12 with pressure.
In FIG. 10, the feeding and separating roller 3 and the registration rollers 5 are made in independent unitized bodies, and a multiplicity of parts makes it difficult to design a compact size configuration as a result. Further, there is required to provide an independent drive transmission mechanism in each unitized body because the feeding amount and a conveying speed for the sheet have to be controlled in each unitized body. Therefore, construction and synchronization of the parts of the apparatus is complex as a result.
From a point of compact sizing, the sheet feeding apparatus which is shown in FIG. 11 is improved because the sheet feeding roller 10 and the driven sheet conveying roller 12 are mounted on the same shaft in the sheet feeding apparatus. However, a drive force transmission mechanism for the drive sheet conveying roller 14, independent from a drive force transmission mechanism of the sheet feeding roller 10 is needed, and a number of parts is not reduced because the sheet feeding roller 10 and the drive sheet conveying roller 14 are both required to be provided. Accordingly, reducing a number of parts is not realized.